Rhodium (II) complex represented by Rh2(OAc)4 easily decomposes α-diazocarbonyl compound under much milder condition than transition metals such as cupper and complex of transition metal, to generate rhodium (II) carbene intermediate, although its structure has not been proved.
Carbene carbon in rhodium (II) carbene intermediate shows extremely high electrophilicity and there are various reactions based on the intermediate. The reaction includes, for example, addition to carbon-carbon multiple bond, insertion to C—H and X—H (X═N, O, S, Se, Si and the like) bonds or rearrangement and additional cyclization reaction triggered by ylide formation, etc. All of the above reactions are catalytic reactions and they are important reactions in synthetic chemistry because of simultaneous formation of carbon-carbon bond formation and generation of asymmetric carbon (Reference 1).
Rh2(OAc)4 may easily replace acetato, a bridging ligand, with various carboxylato and amidato by a ligand exchange reaction, and may synthesize rhodium(II) complexes with various characteristics. For example, Doyle et al. developed asymmetric amidato complex Rh2(5S-MEPY)4, Rh2(4S-MPPIM)4 and the like with fixed asymmetric space (Reference 2). The present complex has high enantio selectivity in intramolecular C—H insertion reaction of α-diazoacetato or α-diazoacetamide and intramolecular cyclopropane formation reaction thereof. McKervey, Davies et al. developed rhodium (II) carboxylato complex, wherein allenesulfonylprolinato was incorporated in bridging ligand. Particularly, Rh2(S-DOSP)4 developed by Davies et al. accomplished extremely high enantio selectivity in intermolecular C—H insertion reaction of phenyldiazoacetato or vinyldiazoacetato and intermolecular cyclopropane formation reaction thereof performed in hexane (Reference 3).
The present inventors developed rhodium (II) carboxylato complex integrated with optically active N-phthaloylamino acid as a bridging ligand and reported intramolecular asymmetric C—H insertion reaction and asymmetric additional cyclization and rearrangement reaction via ylide formation by the use of various α-diazocarbonyl compounds as substrates (Reference 4).
Asymmetric catalytic reaction by homogeneous transition metal complex has often difficulties in separation and purification between catalysts and products after the reaction. Particularly, the field including medications, cosmetics and foods necessitate to remove strictly heavy metal from products. Furthermore, there are economical problems in applying to large-scale synthesis, since the complex needs expensive ligands and metal. Consequently, development of removal method of metal complex or recoverable and reusable catalysts has been actively performed (Reference 5).
One of the solution concerning removal, recovery and reuse of rhodium (II) complex includes supporting of rhodium (II) complex immobilized in insoluble solid-phase carriers. Use of solid-phase rhodium (II) complex enables theoretically easy separation from products, recovery and reuse of expensive rhodium complex, and prevention of metal from releasing. For example, Doyle et al. developed rhodium (II) amidato complex Rh2(S-PYCA)4, whose bridging ligand is pyrrolidinone-5(S)-caroxylato incorporated with soluble polyethylene. They are successful in reusing the complex several times maintaining good asymmetric yield in intramolecular asymmetric C—H insertion reaction of α-diazoacetato (Reference 6). Moreover, Davies et al. paid attention to the property of binuclear rhodium (II) complex, whose axial position is occupied by various Lewis basic axial ligands, and proposed a supporting method, wherein Rh2(S-DOSP)4 and various rhodium (II) complexes are coordinated with pyridines on solid-phase. In intermolecular asymmetric C—H insertion reaction of phenyldiazoacetato, they found that solidified Rh2(S-DOSP)4 catalyst showed catalytic activity and asymmetry discriminative ability similar to those by Rh2(S-DOSP)4 alone (Reference 7). While, Biffis et al. developed a catalyst, wherein rhodium (II) perfluorocarboxylato complex is supported by silica gel incorporated with perfluoroalkyl chains, and accomplished recovery and reuse of the catalysts in silanization reaction of alcohols (Reference 8).    Reference 1: Synthesis, 2003, 1137-1156.    Reference 2: Chem. Rev. 1998, 98, 911-935.    Reference 3: Chem. Rev. 2003, 103, 2861-2903.    Reference 4: Adv. Synth. Catal. 2005, 347, 1483-1487.    Reference 5: Chem. Rev. 2002, 102, 3275-3300.    Reference 6: J. Org. Chem. 1992, 57, 6103-6105.    Reference 7: Org. Lett. 2003, 5, 479-482.    Reference 8: Green Chem. 2003, 5, 170-173.